Process for the manufacture of oxygenates

ABSTRACT

α-Hydroxycarbonyl compounds are obtained from aldehydes or ketones by forming an acetal or ketal which is decomposed to a vinyl ether. The ether is selectively oxidized under conditions yielding an α-hydroxy-aldehyde or α-hydroxy-ketone with the carbonyl group protected. The last-mentioned compounds are valuable sources for other functional organic molecules, for example lactic acid.

This Application is the U.S. National Stage Application ofPCT/EP97/02124 filed Apr. 23, 1997.

This invention relates to processes for the manufacture of organiccompounds, and more especially to the manufacture of oxygenates ofhydrocarbons.

In the industrial preparation of functional organic compounds, it isdesirable that a given reaction proceeds in good yield and highspecificity. There are numerous routes to organic molecules containing ahydroxy group. The yield resulting from a number of such routes is,however, not high, and environmentally acceptable effluent disposal andseparation of the product from by-products add to costs.

The need for an improvement in manufacturing processes is exemplified bylactic acid production.

Lactic acid, 2-hydroxypropionic acid, and its derivatives, especiallysalts and esters, have many industrial uses, primarily in the foodindustry but also increasingly in the manufacture of biodegradablepolymers. Much of the product has long been obtained by fermentation ofhexoses or hexose-producing raw materials, a procedure from which muchunwanted by-product and effluent result; known synthetic methods, forexample using acetaldehyde, propene, or propionic acid, as startingmaterials, have grown in commercial importance but they too present someenvironmental problems, and yields admit of improvement.

As discussed in Chemistry in Britain, December 1996, 45, the lactic acidproduced by fermentation is neutralized as it is produced by calciumcarbonate and, to keep the salt in solution so that it may be separatedfrom residues by filtration, its concentration has to be kept low,resulting in high plant capacity requirements and hence costs. Theworkup, including carbon treatment, evaporation and sulphuric acidtreatment, produces stoichiometric quantities of calcium sulphate, andthe resulting lactic acid is only of technical grade. Purificationentails esterification, distillation and hydrolysis, with theirassociated waste production. If chemical synthesis is used, acetaldehydeis treated with HCN to give lactonitrile, which is hydrolysed usingsulphuric acid resulting in the low value product ammonium sulphate.Again, for purification, the crude acid has to be esterified and theester hydrolysed. Both commercial procedures are therefore costly inenergy and, inter alia, waste disposal.

There are also numerous synthetic routes by which a hydroxy group may beintroduced into a ketone. For example, hydroxyacetone, a molecule withnumerous uses as an intermediate in food, fine chemicals andpharmaceutical preparation and elsewhere, for example, as a solvent, istypically made by bromination of acetone and nucleophilic replacement ofthe bromine substituent by a hydroxy group. Environmentally acceptableeffluent disposal and separation of the desired product from by-products(which here include the aldol condensate typically resulting in thealkaline environment prevailing) again add to costs.

There clearly remains a need for a better synthetic route to manyhydroxy-substituted carbonyl compounds.

In “Zeolites: A Refined Tool for Designing Catalytic Sites”, edited byBonneviot and Kaliaguine (Elsevier, 1995) Yang and Wang describe theelimination of methanol from dimethylacetal, forming methyl vinyl ether,over aluminophosphate molecular sieves and zeolites.

In Synthesis, August 1977, p 578, Frimer describes the preparation of anα-hydroxy acetal by peracid epoxidation of the corresponding enol etherin an alcoholic solvent.

In U.S. Pat. No. 5,354,875 there is disclosed the epoxidation ofolefins, including vinyl ethers, using a mixture of titanium silicaliteand titania.

In this specification, the term “vinyl ether” is used to denote acompound in which one of two carbon atoms joined by an olefinic bond islinked to the ether oxygen.

The present invention provides a process for the manufacture of anα-hydroxy aldehyde or ketone in which the carbonyl group is protectedwhich comprises (a) forming an acetal or ketal by reaction of analdehyde or ketone and an alcohol or an ortho-ester, (b) decomposing theacetal or ketal to form a vinyl ether, and (c) oxidizing the vinyl etherin the presence of a carbonyl group-protective reagent to form theα-hydroxy aldehyde or ketone with the carbonyl group protected.

The reaction, step (a), between the aldehyde or ketone and the alcoholis desirably carried out with the alcohol in molar excess,advantageously in at least twice molar proportions for a monohydroxyalcohol, preferably in a molar proportion of aldehyde:alcohol within therange of from 1:2 to 1:10 and more preferably from 1:2 to 1:6. Althoughnot at present preferred, a dihydroxy alcohol may be used, in which caseequimolar proportions suffice. While an elevated temperature facilitatesrapid reaction and good conversion, any temperature within the range offrom room temperature to 120° C., preferably about 100° C., may be used,advantageously at autogenous pressure.

As aldehyde, there may be mentioned, more especially, an aliphaticaldehyde, for example, acetaldehyde, propanal, a butanal, a pentanal ora hexanal, or an araliphatic aldehyde, e.g., phenylacetaldehyde. Asketone, there may be mentioned, more especially, an aromatic ketone, forexample, acetophenone.

As the alcohol there may be mentioned more especially aliphaticalcohols, preferably saturated aliphatic alcohols, for example,methanol, ethanol, 1-propanol, as monohydroxy alcohols, and ethyleneglycol as a dihydroxy alcohol. Alcohols having more than two hydroxygroups may be used, but are not at present preferred.

For ketal formation, the use of an ortho-ester is preferred to the useof an alcohol, e.g., ethyl orthoformate, CH(OC₂H₅)₃ may be used withgood results.

The formation of the acetal or ketal is desirably carried out in thepresence of a metallic halide, e.g., an alkaline earth halide, e.g.,calcium chloride, or an acid catalyst, either heterogeneous orhomogeneous e.g., a mineral acid, a Lewis acid, or a molecular sieve inacid form. Advantageously, a heterogeneous catalyst is used; as examplesthere may be mentioned a molecular sieve, for example, a siliconaluminophosphate, e.g., SAPO-5, 11 or 34, or, preferably, a zeolite,e.g., H-β, HMCM-41, H-Mordenite, H-Faujasite, or H-ZSM-5. A molecularsieve of the higher acidity represented by the zeolite examples ispreferred, as is one that, like the zeolites, is relatively hydrophobic.

The molecular sieve may be used on a support, e.g., of silica oralumina, and dry silica gel and alumina may themselves be activecatalysts in this reaction, as described by Kamitori, et al, TetrahedronLetters, 26, 39, 4767 (1985).

The reaction may be carried out at room temperature or, preferably, anelevated temperature, advantageously of at least 80° C., preferably atleast 100° C., in the liquid or gaseous phase, the liquid phase reactionbeing preferred, giving high conversion and selectivity.

The resulting acetal or ketal may readily be decomposed, step (b), byelimination of one molecule of alcohol to form a vinyl ether or by ringopening if the acetal is formed by a dihydric alcohol. Decomposition maybe effected by pyrolysis, for example, by heating in an inert atmosphereat a temperature within the range of from 150 to 500° C., moreespecially from 250 to 400° C. A WHSV within the range of from 0.1 to100, if desired or required using a catalyst, may conveniently be used.As catalysts there may be mentioned a supported noble metal catalyst,e.g., silver or platinum on silica or alumina, an acid catalyst, e.g.,phosphorus pentoxide or p-tosyl acid, or, preferably, a molecular sievecatalyst. As molecular sieve, a weakly acid, medium or small porematerial is preferred, e.g., Na-Mordenite, SAPO-34 and AlPO₄-11. U.S.Pat. Nos. 4,891,451, 5,100,852, and 5,105,022, the disclosures of whichare incorporated herein by reference, propose various catalysts (e.g.,Mordenite, ZSM-5, borosilicate and iron silicate zeolites, and phosphatemolecular sieves) for a reaction of this type.

If desired, steps (a) and (b) may be combined, in a process in which analdehyde or ketone and an alcohol are reacted under conditions in whicha vinyl ether results. While not wishing to be bound by any theory, itis believed that an acetal or ketal resulting from an initial reactionis decomposed by an elimination reaction to yield the ether. In anyevent, any intermediate, whatever its nature, need not be isolated.Advantageously, to effect direct vinyl ether formation, the reaction maybe carried out at a temperature within the range of 200° C. to 400° C.Advantageously, a molar ratio of alcohol:aldehyde or ketone within therange of from 2:1 to 16:1 is employed. Advantageously, a catalyst asdescribed above with reference to step (a) or step (b), and preferablywith reference to step (a) is employed.

As indicated above, reaction of the vinyl ether, to introduce a hydroxygroup on the carbon atom of the double bond remote from the etheroxygen, step (c), is effected in the presence of an oxidizing agent anda compound that forms a bond with the carbon atom linked to the etheroxygen and provides a proton to the molecule. Such a protic masking orprotecting compound may be, for example, an acid, especially acarboxylic acid, an amine, a thiol, or, advantageously, an alcohol, inwhich case the resulting product is an α-hydroxy acetal or ketal.

The alcohol is advantageously a low-boiling alcohol, e.g., ethanol,methanol or n-propanol. The alcohol is advantageously present in atleast a stoichiometric quantity, advantageously in a molar ratio of atleast 5:1, preferably at least 10:1, and most preferably at least 40:1.The reaction may be carried out in solution, in which case an excess ofalcohol reactant may conveniently act as solvent.

Oxidation of the vinyl ether in the presence of an alcohol to form anα-hydroxy acetal or ketal may employ the same alcohol as in theformation of the initial acetal, or a different alcohol. As oxidizingagent, which may if desired be generated in situ, there may bementioned, for example, a peroxy acid, e.g., a perbenzoic acid such, forexample, as a chloroperbenzoic acid, perpropionic acid, hydrogenperoxide, or an organic hydroperoxide, for example tert-butylhydroperoxide (TBHP). Alternatively, an inorganic oxidant may be used.Examples include persulphates and hypochlorites.

Advantageously, an oxidation catalyst is employed, either a homogeneousor, preferably, a heterogeneous catalyst being suitable, for example, ametal oxide deposited on an amorphous support, e.g., silica, or a metalaerogel or xerogel. A heteropolyanionic acid catalyst is also suitable,for example, a polyoxometallate of the general formula XM₁₂O₄₀ ^(x-8)wherein M represents a metal ion, e.g., Mo(VI), W(VI) or V(V), Xrepresents P(V) or Si(IV) and x represents the oxidation state of theatom X. (See Cat. Rev. Sci. Eng. (1995) 37(2), 311 to 352).

Another suitable catalyst is a tetranuclear manganese complex or atetranuclear metal complex having a mixed metal core, as described inU.S. Pat. Nos. 5,025,101 and 5,504,256, the disclosures of which areincorporated herein by reference. Preferably, a transition metal oxidecatalyst in a high oxidation state, e.g., Mo(VI), W(VI), Ti(IV), Cr(VI),Zr(IV), V(V), Os(VI), Se(IV), Re(IV, VI, and VII) and Ru(VI and VIII),or a molecular sieve, especially a metal-containing, more especially atitanium-containing, molecular sieve, especially one in which at leastpart of the metal forms part of the structure of the molecular sieve, isused. Most preferably a Ti-silicalite, e.g., TiMCM-41, TS-1, or TS-2, orTiSAPO or TiAPO, or a zeolite, e.g., Ti-β, is used. Advantageously, themolecular sieve contains an alkali metal or other small radius cation,e.g., K, Na, or, preferably, Li. Reaction conditions vary with thecatalyst and oxidant. A temperature in the range of room temperature to150° C., preferably 40° C. to 100° C., at reaction times of from 30minutes, especially 1 hour, to 10 hours, may typically be used.

The invention also provides processes in which the product of step (c),the protected aldehyde or ketone, is further treated to yield othervaluable types of molecules.

Among these, there may more especially be mentioned processes in which:

(d) the protected aldehyde or ketone is hydrolysed to the correspondingunprotected α-hydroxy aldehyde or ketone;

(e) the protected aldehyde is hydrolysed to the correspondingunprotected aldehyde and in a second step

(f) is oxidized to an α-hydroxy acid,

(g) the protected aldehyde is hydrolysed and oxidized in a single stepto an α-hydroxy acid.

(h) the protected aldehyde is oxidized to an α-aldehydic (α-formyl)acid,

(j) the protected aldehyde is hydrolysed and rearranged to an α-hydroxyketone,

(k) the protected aldehyde is oxidized to an α-keto (α-oxo) acetal,which is optionally,

(l) hydrolysed to an α-keto (α-oxo) aldehyde, which is optionally,

(m) oxidized to an α-keto (α-oxo) acid.

The protected α-hydroxyaldehyde or ketone may be hydrolysed, step (d),if desired in situ, by a number of different routes. For example, acidhydrolysis provides an α-hydroxyaldehyde or ketone, using a dilutemineral acid or an ion exchange resin or a molecular sieve in acid form.Hydrolysis using dilute sulphuric acid is described by A. Wohl,Berichte, 1908, 3599 at 3608, using 0.1 N sulphuric acid for 3 days atroom temperature.

At a given temperature, overall conversion is enhanced as the mole ratioof water to hydroxyacetal is increased to about 20:1, as is the molarproportion of 2-hydroxyaldehyde formed. Advantageous molar ratios are inthe range of 5:1 to 20:1. Since the competing reaction (i) isomerizationof the hydroxyaldehyde to a hydroxyketone, takes place under hydrolysisconditions, reaction times are advantageously limited as much as isconsistent with good conversion if the aldehyde is required.

Overall conversion increases with catalyst concentration, as does therate of isomerization to hydroxyketone. Accordingly, moderate catalystconcentrations, e.g., up to 5 wt %, based on acetal, are used if thealdehyde is required.

While higher temperatures, e.g., up to 90° C., improve conversion, theyalso favour hydroxyketone yield, and a temperature up to 70° C. ispreferred if the aldehyde is required.

If recovery of the α-hydroxy aldehyde is required, this may be effectedby distillation or solvent extraction. Alternatively, the reactionmixture may be oxidized without separation of the aldehyde, the latterbeing selectively oxidized.

The now unprotected aldehyde may be oxidized, step (f), e.g., bymolecular oxygen, air, or a hydroperoxide. The oxidation may be carriedout in the presence of a catalyst, e.g., a supported noble metal (forexample, silver, palladium or platinum), catalyst.

Alternatively, the protected α-hydroxyaldehyde may be hydrolysed andoxidized in a single step (g), to an α-hydroxy acid. This may in turn bedehydrated to yield an α-olefinic acid, or esterified, or reacted toform a salt or an amide. The α-hydroxy acid is advantageously lacticacid. In a preferred embodiment of the invention as represented byprocesses in which steps (e) and (f) are, or step (g) is, carried out,the invention provides a process for the manufacture of lactic acidwhich comprises forming an acetal by reaction of propanal and analcohol, decomposing the acetal to form a propene ether, oxidizing theether in the presence of an aldehyde group-protecting reagent to yield aprotected 2-hydroxypropanal and removing the protection from thealdehyde group and oxidizing the resulting 2-hydroxypropanal to formlactic acid.

It will be appreciated that this reaction sequence corresponds to steps(a) to (d) and either (e) and (f) or (g) or the general reactionsequence above, and that the reactions and conditions exemplified forthe general reaction are suitable or preferred for the manufacture oflactic acid.

As indicated above, lactic acid is a valuable product itself, and may beused in the manufacture of valuable low-toxicity solvents for example byesterification. Examples of lactic acid esters are the methyl, ethyl andlinear and branched C₃ to C₈ alkyl esters, especially isopropyl,n-butyl, and 2-ethylhexyl esters. There may also be used as esterifyingalcohols the commercially available Exxal (trade mark) alcohols, whichare mixtures of mainly branched alkanols, with, e.g., 7 to 13 carbonatoms.

The processes according to the invention may be carried out with goodyields and selectivity to the desired products, with the variousprotective materials being recyclable.

If the protected α-hydroxyaldehyde, especially the 2-hydroxyacetal, isoxidized without hydrolysis, an α-aldehydic acid may be formed.

Step (j), the hydrolysis and rearrangement of a protected aldehyde to anα-hydroxyketone is a valuable process per se. The present inventionaccordingly also provides a process for the manufacture of anα-hydroxyketone which comprises hydrolysing an α-hydroxyaldehyde inwhich the carbonyl group is protected and rearranging (isomerizing) theresulting α-hydroxyaldehyde to an α-hydroxyketone, the process beingcarried out in the presence of an acid catalyst. In this aspect of theinvention, the α-hydroxyaldehyde may be an aliphatic or araliphaticaldehyde, for example, glycolaldehyde, an α-hydroxy substituted propanalor, linear or branched, butanal, pentanal or hexanal. As indicatedabove, the aldehyde group may be protected by, for example, an acid,especially a carboxylic acid, an amine, a thiol or, advantageously, analcohol, in which case the protected molecule is an acetal, to whichreference will hereinafter be made for simplicity. As protecting alcoholthere is advantageously employed a low-boiling alcohol, for examplemethanol, ethanol, or n-propanol.

As examples of suitable acid catalysts there may be mentioned inorganicor organic acids, ion exchange resins and molecular sieves. Homogeneousor heterogeneous catalysts may be used. As inorganic acid catalysts, forexample, there may be mentioned sulphuric, hydrochloric acid, includingLewis acids, while as organic acid there may be mentioned for example,acetic acid.

As molecular sieve there may be mentioned, for example, a siliconaluminophosphate, e.g., SAPO-5, 11 or 34, or, preferably, a zeolite,e.g., H-β, H-Mordenite, H-Faujasite, or H-ZSM-5. A molecular sieve ofthe higher acidity represented by the zeolite examples is preferred, asis one that, like the zeolites, is relatively hydrophobic.

The molecular sieve may be used on a support, e.g., of silica oralumina.

As indicated above with reference to reaction (d), at a giventemperature, although the hydrolysis reaction is enhanced as the moleratio of water to hydroxyacetal is increased to about 20:1, therearrangement (isomerization) is inhibited, resulting in a lowerproportion of α-hydroxyketone compared with remaining α-hydroxyaldehyde.Advantageous molar ratios are therefore in the range of 1:1 to 10:1 ifthe hydroxyketone is required. The longer the reaction time, the greaterthe extent of isomerization from α-hydroxyaldehyde to α-hydroxyketone.

An acetal:catalyst ratio in the range of from 1:1 to 1000 to 1 by weightmay conveniently be used. The rate of isomerization to hydroxyketoneincreases with catalyst concentration. Accordingly, relatively highcatalyst concentrations, e.g., in the range of from 10 to 20 wt %, basedon acetal, are in this case preferred.

The process of this aspect of the invention may be carried out in theliquid or the gaseous phase. Higher temperatures, e.g., up to 100° C.,improve conversion, and also favour hydroxyketone yield, and atemperature in the range of from 70° C. to 90° C. is preferred.

Recovery of the desired α-hydroxyketone from unreacted startingmaterials and α-hydroxyaldehyde may be effected by, for example,distillation or solvent extraction.

As an example of steps (k) to (m) above, oxidation of an α-hydroxyacetalto an α-ketoacetal, its hydrolysis to an α-ketoaldehyde, and itsoxidation to an α-keto acid, there may be mentioned the transformationof 2-hydroxy-1,1-dimethoxypropane to pyruvic acid.

An aldehyde required as starting material for the aldehyde-relatedprocesses of the invention may readily be produced by hydroformylationof an olefin, if desired in a dilute feedstream.

The following Examples illustrate the invention:

Step (a)—Acetal Formation

EXAMPLE 1

Methanol (2.0 moles) and anhydrous calcium chloride (0.16 mole) weremixed in a glass vessel under nitrogen. An exotherm took the temperatureto about 40° C., and the vessel was placed in an ice bath to cool it toabout 4° C. Propanal (1.0 mole) at 4° C. was slowly added with continuedcooling, the reaction mixture being stirred and cooled for 24 hours. GC,IR, and NMR analysis showed an 86.7% conversion and 100% selectivity to1,1-dimethoxypropane.

EXAMPLES 2 to 7

These examples employed acid molecular sieves as catalysts. Propanal andmethanol were mixed at a molar ratio of 1:8. In each Example, 20 g ofreaction mixture were employed together with 0.15 g of catalyst. Thereaction mixture was heated in a closed vessel to 100° C. and maintainedat that temperature for 1 hour. The acetal 1,1-dimethoxypropane waspurified by distillation. Analysis as in Example 1 indicated theconversion of propanal and selectivities achieved; Table 1 gives theresults.

TABLE 1 Example Catalyst Conversion % Selectivity % 2 H-β 92 100 3HMCM-41 87 100 4 H-ZSM-5 91 100 5 SAPO-5 79 100 6 SAPO-11 77 100 7SAPO-34 80 100

EXAMPLES 8 to 11

Part of a 60 cm long tubular reactor, diameter 18 mm, was filled with3.3 mm diameter glass beads and the remainder, 20 cm, with a mixture ofthe glass beads and catalyst. The catalyst was prepared by pelletizing a30% H-β zeolite and 70% (by weight) gamma-alumina binder mixture,calcining the pellets at 550° C. for 10 to 16 hours, crushing, and usingthe fraction between 1 and 2 mm. The reactor was placed in a tubularoven and heated at the temperatures indicated in Table 2 below. Areaction mixture of propanal:methanol at a molar ratio 1:16.4 is passedthrough the reactor at 1 ml/minute in admixture with argon at the rateshown.

TABLE 2 Ex. Temperature Argon Gas Conversion Selectivity, % No. ° C.Flow ml/min. % to Acetal to Ether  8 200 10 27.2 52 13.8  9 300 10 43.41.9 21.9 10 150  5 45.2 100 0 11 150 10 51.7 86.6 0

Examples 8 and 9 illustrate that if desired steps (a) and (b) may becombined.

Step (b)—Preparation of Propenyl Ether

EXAMPLES 12 and 13

A tubular reactor, of diameter 18 mm and length 50 cm, was filled with185 g of 3 mm glass beads, and heated in a tubular oven to thetemperatures shown in Table 3. 1,1-dimethoxypropane was fed to the ovenat 1 ml/minute together with 10 ml/minute argon, an HSV of 0.27 l/h. Theconversion and selectivity to 1-methoxypropene are given in Table 3.

TABLE 3 Example 12 Example 13 Reaction Temperature, ° C. 300 400Selectivity to propenyl ether, % 100 100 Conversion, %  26  86 Cis:TransRatio 1:2 1:2

Step (c)—Oxidation to α-hydroxyacetal

EXAMPLE 14

10 g (0.3 mol) of methanol were mixed with 7 mmol of 1-methoxy propeneand cooled to 8° C. 7 mmol of 3-chloroperoxybenzoic acid were added over40 minutes with continued cooling, and then the temperature wasincreased to room temperature and maintained for 30 minutes. GC and NMRanalysis showed 100% conversion, of which 70.6 mol % was to2-hydroxy-1,1-dimethoxypropane (hydroxyacetal) and 29.4 mol % was to1,1-dimethoxypropane.

EXAMPLE 15

5 g (0.16 mol) of methanol were mixed with 5 mmol H₂O₂ (30% in H₂O) and20 mmol of 1-methoxypropene. 0.25 g of TS-1 were added, and the mixtureheated at 40° C. for 2 hours. Analysis showed 98% conversion of H₂O₂ and46% conversion of the methoxypropene, of which 54 mol % was to2-hydroxy-1,1-dimethoxypropane and 46 mol % was to 1,1-dimethoxypropane.

EXAMPLE 16

5 g (0.16 mol) of methanol were mixed with 14 mmol of 1-methoxypropeneand 14 mmol of TBHP (80% in di-tert butylperoxide). 0.1 g TiMCM-41 wereadded and the mixture heated at 100° C. for 1 hour. 99% of both themethoxypropene and the TBHP were converted; the molar selectivity was56% to hydroxyacetal, 38% to 1,1-dimethoxypropane and 8% to1-methoxy-1-perbutoxypropane.

EXAMPLE 17

10 g (0.3 mol) of methanol were mixed with 10 mmol of TBHP (80% indi-tert butyl peroxide) and 40 mmol of 1-methoxypropene. 1 mmol ofMo(CO)₆ was added, and the mixture heated at 50° C. for 3 hours. Theconversion of TBHP was 100%, and that of 1-methoxypropene was 61.5%, ofwhich the molar selectivity was 41.5% to α-hydroxyacetal and 58.5% to1,1-dimethoxypropane. The efficiency of the TBHP was 100%.

EXAMPLES 18 to 23

In these examples, the effect on vinyl ether oxidation (step c) ofion-exchanging the acid form of the Ti-containing catalyst with a cationof small ionic radius was examined. Ion-exchange was effected using a 1%by weight lithium acetate solution, 0.5 g of catalyst in the acid formbeing added to 10 ml of solution. The resulting slurry was heated to 80°C. and maintained at that temperature for 30 minutes with stirring.After cooling to room temperature, the slurry was centrifuged at 12,000r.p.m. Treatment of the catalyst was repeated twice, and the resultingproduct washed with water at 80° C. three times and then with methanolat 40° C. three times. The catalyst was dried at 120° C. and calcined at500° C. Four catalysts were treated in this way.

Catalyst 1—Tiβ made by the procedure of International Application WO94/02245. 1H is original (hydrogen) form, 1Li is lithium form.

Catalyst 2—Tiβ made generally by the procedure of J. Chem. Comm. 1992,589. 2H is original form, 2Li is lithium form.

Catalyst 3—TiMCM-41 made by the procedure of J. Chem. Soc. Chem. Comm.1994 (A. Corma et al). 3Li is lithium form.

Catalyst 4—TS-1. 4Li is lithium form.

In each case, 5 g (0.16 mol) of methanol were mixed with 5 mmol of H₂O₂(30% in H₂O) and 20 mmol of 1-methoxypropene. 0.25 g of catalyst wereadded, and the mixture heated at 40° C. for 40 minutes. Table 4 belowsummarizes the results.

TABLE 4 Efficiency, Ether Selectivity to Ex. Catalyst Conv, % % Conv, %HO-acetal Acetal 18 1H  33  91 100 7.5 92.5 19 1Li  97  82 86.4 23 77 202H  15  98 100 3.6 96.4 21 2Li 100 100 75 34 66 22 3Li 100 100 83.3 3070 23 4Li 100 100 28.2 88 12

In the table above, “Conv.” indicates the percentage of H₂O₂ added thatis consumed, while “Efficiency” indicates the percentage of thatconsumed which is used in formation of the desired product.

Step (d)—Hydrolysis of Hydroxyacetal and Oxidation to Lactic Acid—2stage—Examples 24 to 30

Part 1—Hydrolysis;

EXAMPLES 24 to 29

2 g of 2-hydroxy-1,1-dimethoxypropane were mixed with 20 g of water inthe presence of an acid catalyst. In Example 24, the temperature wasmaintained at room temperature for 5 days, while in Examples 25 to 29the reaction mixture was maintained at 60° C. for 5 hours. Table 5 belowindicates the catalyst, catalyst strength, reaction and conversion ineach case.

TABLE 5 Example H⁺/Acetal H⁺ conc No. Acid (molar) (mol/l) Conv. % 24H₂SO₄ 1/33  0.05   100 25 H₂SO₄ 1/500 0.00075 100 26 H₂SO₄ 1/250 0.00150 99 27 H₂SO₄ 1/100 0.00375 100 28 Amberlyst 15 —  4 g/l  99 29 ZeoliteHB — 50 g/l 100

“Amberlyst” is a trade mark for an ion exchange resin.

EXAMPLE 30

Hydroxypropanal was oxidized with oxygen at atmospheric pressure in a 50ml flask equipped with a stirrer, condenser and port for gas inlet.Hydroxypropanal solution (2 g in 20 ml water) and a 5% platinum oncarbon catalyst (0.1 g) were loaded into the flask with stirring at 60°C. Oxygen was bubbled for 5 hours, the oxidation reaction startingimmediately. Reaction rate and product distribution were measured byoxygen consumption, HPLC, and NMR. The results showed 44.4% conversionwith a selectivity to lactic acid of 92.4% The only by-product resultedfrom the further oxidation of lactic acid or hydroxyacetone to pyruvicacid 7.6%).

EXAMPLES 31 to 33

Hydroxypropanal was oxidized with molecular oxygen in a glass reactorequipped with a magnetic stirrer, gas distributor, and combinedthermometer and pH sensor. The catalyst (0.7 g platinum on carbon,pretreated as described in J. Chem. Soc. Chem. Comm. 1995, 1377)hydroxypropanal (5.18 g, 88% pure, 61.6 mmol, remainder hydroxyacetone),and 70 g water were loaded into the reactor and heated to 60° C. undernitrogen, which was then replaced by oxygen flow. The pH was adjustedwith 3.5M KOH or 1.75M Na₂CO₃, in the case of KOH by automatictitration. The results are shown in Table 6.

TABLE 6 Time, Conv Selectivity mol % Example pH, using hr % LA PA AA HA31 10, KOH 3 100 74 7.6 3 15.4 32 8-9, Na₂CO₃ 2.5  99 90 0.2 6  3.8  33*7.3, KOH 3  93 79 0.2 0 15.6 *Other, unknown, species produced. LA:lactic acid   AA: acetic acid PA: pyruvic acid  HA: hydroxyacetone.

Steps (d) and (g)—Single stage Oxidative Hydrolysis of Hydroxyacetal toLactic Acid

EXAMPLE 34

1.8 g of 2-hydroxy-1,1-dimethoxypropane were mixed with 10 g water, 0.2g of a 5% platinum on carbon catalyst, and 0.1 g of an acidic ionexchange resin, Amberlyst 15, in a 30 ml flask equipped with stirrer,condenser, and gas inlet port. Oxygen at atmospheric pressure was passedthrough the reaction mixture for 23 hours at room temperature. Analysisshowed 87% of the hydroxyacetal was converted, with molar selectivity of30% to lactic acid, 68% to hydroxypropanal, and 0.5% to pyruvic acid.

Steps (d) and (i)—Hydrolysis to α-hydroxyaldehyde and ketone

EXAMPLES 35 to 48 Hydrolysis of Hydroxyacetal to 2-Hydroxypropanal andHydroxyacetone

In these examples the effects of varying the reaction conditions onconversion and selectivities (given below in molar %) are observed.First, the effect of the molar ratio of water:substrate (hydroxyacetal)was investigated. The results are shown in Table 7.

TABLE 7 Time, hours 1 3 5 1 3 5 1 3 5 Ex. Molar ratio Conversion,OH-Propanal, OH-Acetone, No. water:substrate % % % 35  5:1 20 68  82  8770 63 13 30 37 36 10:1 24 78  92  93 84 72  8 16 28 37 20:1 32 93  98100 83 74  0 17 26 38 50:1 16 83 100 100 91 85  0  9 15

Reaction Conditions: Catalyst Concentration 5 wt %, H-β, Si:Al ratio28:1. Temperature 70° C.

Second, the effect of varying the weight ratio of catalyst:substrate wasinvestigated. Results are shown in Table 8.

TABLE 8 Time, hours 1 3 5 1 3 5 1 3 5 Ex. Wt, %, catalyst Conversion,OH-Propanal, OH-Acetone, No. to substrate % % % 39  1  0  8  17 — 100 91—  0  9 40  5 32 93  98 100  83 74  0 17 26 41 10 56 97  99  93  70 56 7 30 44 42 20 96 99 100  78  41 23 22 59 77

Reaction Conditions: Molar Ratio Water:Substrate 20:1, Catalyst as inExample 26, Temperature 70° C.

Next, the effect of temperature was investigated. Results are as shownin Table 9.

TABLE 9 Time, hours 1 3 5 1 3 5 1 3 5 Ex. Temperature, Conversion,OH-Propanal, OH-Acetone, No. ° C. % % % 43 22  0  8  17 — 100 91 —  0  944 50 24 94  98  93  83 71  7 17 29 45 70 31 93  98 100  83 74  0 17 2646 90 95 99 100  85  50 29 15 50 71

Conditions as in Example 31, but with variation of temperature.

The effect of changing the catalyst to ZSM-5, Si:Al ratio 30:1, underconditions similar to those of Example 46 was examined; the results areshown in Table 10.

TABLE 10 Time, hours 1 3 5 1 3 5 1 3 5 Ex. Conv, OH-Propanal,OH-Acetone, No. Catalyst % % % 47 H-β 95 99 100 85 50 29 15 50 71 48ZSM-5 17 54 100 53 46 32 47 54 68

The examples demonstrate that lactic acid may be produced in good yieldor high selectivity, as desired.

What is claimed is:
 1. A process for the manufacture of an α-hydroxyaldehyde or ketone in which the carbonyl group is protected whichcomprises (a) forming an acetal or ketal by reaction of an aldehyde orketone and an alcohol or an ortho-ester, (b) decomposing the acetal orketal to form a vinyl ether, and (c) oxidizing the vinyl ether in thepresence of a carbonyl group-protective reagent to form the α-hydroxyaldehyde or ketone with the carbonyl group protected.
 2. A process asclaimed in claim 1, wherein the carbonyl group-protective reagent is analcohol.
 3. A process as claimed in claim 1, wherein step (a) is carriedout in the presence of an acid catalyst.
 4. A process as claimed inclaim 1, wherein step (b) is carried out by pyrolysing the acetal orketal.
 5. A process as claimed in claim 1, wherein step (c) is carriedout using a peracid.
 6. A process as claimed in claim 5, wherein step(c) is carried out in the presence of a catalyst.
 7. A process asclaimed in claim 5, wherein step (c) is carried out in the presence of aTi-containing molecular sieve.
 8. A process as claimed in claim 1,wherein the protecting group is removed from an aldehyde or ketone byacid hydrolysis in the presence of a molecular sieve or ion-exchangeresin in acid form.
 9. A process as claimed in claim 8, which is carriedout on an aldehyde, and the aldehyde is simultaneously or subsequentlyoxidized to an α-hydroxy acid using molecular oxygen, and in thepresence of platinum.
 10. A process for the manufacture of lactic acidwhich comprises forming an acetal by reaction of propanal and analcohol, decomposing the acetal to form a propene ether, oxidizing theether in the presence of an aldehyde group-protecting reagent to yield aprotected 2-hydroxypropanal and removing the protection from thealdehyde group and oxidizing the resulting 2-hydroxypropanal to formlactic acid.
 11. A process as claimed in claim 1, wherein a protectedaldehyde is formed, and wherein the protected aldehyde is oxidized to anα-aldchydic acid.
 12. A process as claimed in claim 8, wherein anunprotected aldehyde is formed and wherein it is rearranged to form anα-hydroxy ketone.
 13. A process as claimed in claim 1, wherein aprotected aldehyde is formed, and wherein it is oxidized to an α-ketoacetal.
 14. A process as claimed in claim 13, wherein the α-keto acetalis hydrolysed to α-keto aldehyde.
 15. A process as claimed in claim 14,wherein the α-keto aldehyde is oxidized to an α-keto acid.
 16. A processfor the manufacture of an α-hydroxyketone which the carbonyl group isprotected and isomerizing the resulting α-hydroxyaldehyde to anα-hydroxyketone, the process being carried out in the presence of anacid catalyst.
 17. A process as claimed in claim 16, wherein theα-hydroxyaldehyde is 2-hydroxypropanal, and the isomerization is tohydroxyacetone.
 18. A process as claimed in claim 16, wherein thecatalyst is a zeolite.
 19. A process as claimed in claim 16, whereinhydrolysis is carried out using a water:protected aldehyde molar ratioin the range of from 1:1 to 10:1.
 20. A process as claimed in claim 16,carried out at a protected aldehyde:catalyst weight ratio of from 1:1 to1000:1.
 21. A process as claimed in claim 16, carried out at atemperature within the range of from 70 to 90° C.
 22. A process asclaimed in claim 1, wherein said carbonyl group-protective reagent isprotic.
 23. A process as claimed in claim 1, wherein said carbonylgroup-protective reagent is selected from the group consisting of analcohol, an acid, an amine, a thiol, and a combination thereof.
 24. Aprocess as claimed in claim 23, wherein said alcohol is a dihydroxyalcohol.
 25. A process as claimed in claim 23, wherein said acid is acarboxylic acid.